Axial piston pump having a swash-plate type construction

ABSTRACT

The invention relates to an axial piston pump having a swash-plate type construction, in particular for hydraulic systems, comprising a cylinder drum ( 3 ) which can be rotationally driven about a rotational axis ( 7 ) in a pump housing ( 1 ) and in which pistons ( 9 ) are arranged in an axially displaceable manner, supporting by means of the actuation end thereof ( 11 ) which is accessible from the outside of the cylinder drum ( 3 ), at least indirectly a awash plate ( 15 ), said swash plate can be pivoted by means of an adjusting device ( 21 ) to the desired angles of inclination with respect to the rotational axis ( 7 ) for adjusting, the stroke, of the piston ( 9 ) and also the fluid system pressure generated thereby. Said adjust device comprises an adjusting, piston ( 35 ) in a hydraulically actuated adjusting cylinder ( 31 ), the movement thereof can be transmitted to the awash plate ( 15 ) by means of at least one driven connection comprising a pivot joint ( 37, 39; 29, 43 ), characterized in that the pivot joint is formed by a ball joint ( 37, 39 ) which is arranged between the piston ( 35 ) and the piston and ( 41 ) of the adjusting cylinder ( 31 ).

The invention relates to an axial piston pump having a swash plate type construction, in particular for hydraulic systems, having a cylinder drum that can be driven about a rotational axis, in which pistons are disposed such that they can be displaced axially, which support, at least indirectly, a swash plate with their actuation ends that can be accessed from outside the cylinder drum, which swash plate can be pivoted by means of an adjusting device in order to adjust the stroke of the piston, and thus the fluid system pressure generated therewith, to a desired angle of inclination in relation to the rotational axis, which has an adjustment piston in an adjustment cylinder that can be actuated hydraulically, the movement of which can be transferred to the swash plate via at least one driven connection having a joint.

Axial piston pumps with a swash plate construction are the prior art. They are used widely for supplying pressure to loads such as power cylinders, hydraulic motors and suchlike. Axial piston pumps of the type specified in the introduction, in which the angles of the swash plates in relation to the rotational axis can be adjusted, are distinguished, with respect to likewise known axial piston pumps having stationary swash plates, by a better energy balance during operation. While pumps having stationary swash plates, which function as a fixed displacement pump with a predefined drive rotational rate, always convey a constant volume flow of the fluid, even when no energy is demanded from systems that are actuated by pressure means, and thus must overcome the flow resistances in the hydraulic circuit while running idle, for which drive energy is expended while supplying no useful energy, the pump delivery volume can be set to zero through the adjustability of the swash plate inclination, and the need for drive energy can be minimized. An axial piston pump of the type specified in the introduction is disclosed in DE 44 15 510 C1.

The production costs for the known axial piston pumps of this type are high, because there is a significant engineering effort for the adjustment device having the driven connection, which converts the linear movement of the piston in the stationary adjusting cylinder into an arc-shaped movement of the wash plate.

With respect to these problems, the invention addresses the problem of providing an axial piston pump, the adjustment device of which, for the adjustment of the position of the swash plate, is distinguished by a high operational reliability, with a comparatively simple construction.

In accordance with the invention, this object is achieved by an axial piston pump having the features of claim 1 in its entirety.

Accordingly, a substantial characteristic of the invention is that the joint for the driven connection between the swash plate and the adjustment cylinder is formed by a ball joint located between the piston and the piston rod of the adjustment cylinder. In contrast to a joint connection defining a joint axis, the piston is free of constraining forces, due to the design of the joint in the form of a ball joint.

This leads to less stress on the components, less piston friction with correspondingly less wear, and to a corresponding improvement of the operational reliability.

In particularly advantageous exemplary embodiments, a second joint of the driven connection is formed between the piston rod and an actuating part of the swash plate by a second ball joint, by means of which corresponding advantages are obtained at the coupling point allocated to the swash plate.

The driven connection formed by the ball joints can be designed such that it exhibits no play whatsoever, in that a spring assembly is provided, that retains a ball head and a ball socket of the ball joint in position, in a force-locking manner.

To this end, the assembly can advantageously be formed such that the spring assembly simultaneously pre-loads the wash plate in the pivotal position corresponding to the maximum pump delivery rate. As a result of this double function of the spring assembly, the adjustment cylinder does not need to be configured as a double-action cylinder for generating adjustment movements in both directions, but rather, a single-action adjustment cylinder may be provided, which merely causes an adjustment movement from the pivoted position for maximum pump delivery rate to lower delivery volumes, up to and including zero capacity.

In particularly advantageous exemplary embodiments, a second adjustment cylinder is provided, counter to the first adjustment cylinder and sharing the same cylinder axis, perpendicular to the rotational axis, wherein the adjustment piston of the second adjustment cylinder can be moved hydraulically, counter to the movement of the adjustment piston of the first adjustment cylinder, and the piston rod of the second adjustment cylinder is connected at one end to the associated adjustment piston via a third ball joint, and at the other end, together with the piston rod of the first adjustment cylinder, forms the second ball joint at the actuating part of the swash plate.

In an advantageous manner, the actuating part can be formed by a pivot lever connected to the swash plate, Which extends, laterally to the mash plate and the cylinder drum, parallel to the rotational axis when set to zero pump capacity, and the second ball joint is located at its free end. With this arrangement, the cylinder axis of the adjustment cylinder can be oriented transverse to the rotational axis, in order to move the pivot lever, and thus the swash plate, about a pivot axis via the ball joint located on the end of the pivot lever, which pivot axis runs perpendicular to the rotational axis inside the plane of the sliding surface, on which the pistons of the cylinder drum are supported on the swash plate.

In a particularly advantageous manner, the spring assembly can have a compression spring, which pre-loads the piston rod of the second adjustment cylinder for the movement, which corresponds to the extension of the adjustment piston of the second adjustment cylinder and the retraction of the adjustment piston of the first adjustment cylinder, and thus the pivoting of the pivot lever from the position in which the axes are parallel, toward the position for the maximum pump capacity.

With regard to the actuation of the adjustment device, the assembly can be advantageously made such that the first adjustment cylinder can be subjected to a control pressure for adjusting the pump capacity, and the second adjustment cylinder can be subjected to the prevailing system pressure. As a result, when there is no system pressure, the adjustment device is adjusted to the maximum capacity by the force of the compression spring. When operating the pump with the resulting system pressure, the adjustment remains at the maximum capacity until the adjustment force generated by the control pressure in the first adjustment cylinder exceeds the piston force generated by the system pressure in the second adjustment cylinder, in addition to the spring force, at which point, depending on the control pressure, the swash plate is pivoted back to a lower delivery rate.

For operation with a pressure level limited by control pressure, preferably the piston surface of the piston of the first adjustment cylinder, which can be subjected to control pressure, is selected such that it is larger than the piston surface of the piston of the second adjustment cylinder that can be subjected to the system pressure.

The invention shall be explained in detail below, based on an exemplary embodiment depicted in the drawings. Therein:

FIG. 1 shows a side view of only those components of an exemplary embodiment of the axial piston pump according to the invention that pertain to the adjustment device of the mash plate, wherein the adjustment cylinder of the adjustment device is shown in a cross section;

FIG. 2 shows a longitudinal section of the exemplary embodiment having a cutting plane running through the adjustment device; and

FIG. 3 shows an exploded, extended, perspective, diagonal view of the components of the adjustment device of the exemplary embodiment.

FIG. 1 shows only a part of a pump housing I from the exemplary embodiment that shall be described, which is fully visible in FIG. 2. A cylinder drum 3 is mounted in the housing 1, which can rotate about a rotational axis 7 by means of a drive shaft 5, see FIG. 2. In the typical manner of axial piston pumps, the pistons 9, which are axially displaceable in the cylinder drum 3, are supported via sliding shoes 11 located at their upper ends on the sliding surface 13 of a swash plate 15. This is movably guided at its side facing away from the sliding surface 13 via an arc-shaped swash plate bearing 17 on the pump house 1, such that the mash plate 15 can pivot about a pivot axis 19, which lies in a plane of the sliding surface 13 of the swash plate 15 that runs perpendicular to the rotational axis 7. The swash plate 15 can pivot about the pivot axis 19, by means of an adjustment device, indicated as a whole by the numeral 21, between the pivoted setting shown in FIG. 1, which corresponds to the maximum delivery rate of the pump, and the setting in FIG. 2, for zero pump capacity, wherein in this case, the plane of the sliding surface 13 is horizontal, with respect to the vertical course of the rotational axis 7 in FIG. 2, such that the pistons 9 do not perform a stroke When the cylinder drum 3 rotates.

The adjustment device 21, as the actuating part assigned to the mash plate 15, has a pivot lever 23, which is attached by means of a bolt 25 to the wash plate 15 between two ribs 27 protruding on its lateral surface. The pivot lever 23 extending laterally form the cylinder drum 3 has a ball head 29 on its lower, free end, which is engaged with by control elements of the adjustment device 21, in order to move the pivot lever 23 into the drawing plane, and thus pivot the swash plate 15 about the pivot axis 19.

The adjustment device 21 has a first adjustment cylinder 31, having a cylinder liner 33, in which an adjustment piston 35 is guided. The piston 35 has an inner ball socket 37, which forms a first ball joint together with a ball head 39 on the end of a piston rod 41 allocated thereto. A ball socket 43 is formed on the end of the piston rod 41 opposite the piston 35. The adjustment device 21 has a second adjustment cylinder 45 with a cylinder liner 47, counter to the first adjustment cylinder 31 and sharing the same cylinder axis. A second piston 49, which has a smaller piston surface for pressurization than the opposing first piston 35, is guided therein. As with the first piston 35, a ball socket 51 is formed in the other piston 49, which forms a further ball joint, together with as ball head 53 on the associated piston rod 55. The end of the piston rod 55 facing away from the ball head 53 has a hall socket 57, as is the case with the piston rod 41 of the first adjustment cylinder 31, which ball socket, together with ball socket 43 of the other piston rod 41 and the ball head 29 on the pivot lever 23, forms a ball joint assigned to the pivot lever 23. A compression spring 61 is clamped between the cylinder liner 47 of the second adjustment cylinder 45 and a spring seat 59 of the piston rod 55, which pre-loads the adjustment device 21 in the setting corresponding to the maximum pump capacity shown in FIG. 1, and also holds the ball heads and ball sockets of the three hall joints that have been formed against one another, without play, in the system.

In order to actuate the adjustment device 21, the pressure chamber 63 of the first adjustment cylinder 31 can be subjected to a control pressure that determines the pump delivery rate. The pressure chamber 65 of the second adjustment cylinder 45 is subjected to the system pressure generated during operation of the pump. The force of the compression spring 61, which pre-loads the piston rods 41, 55 for a movement toward the right (corresponding to the depiction in the drawings), retains the adjustment device in the setting for a maximum delivery rate shown in FIG. 1, when the pump is at a standstill, resulting in the second adjustment cylinder 45 not being subjected to any system pressure. In order to adjust the pump to a lower delivery rate during operation, potentially to zero capacity (this setting is shown in FIG. 2), the first adjustment cylinder 31 is supplied with a corresponding control pressure. As soon as the piston force generated by the control pressure in the first adjustment cylinder 31 exceeds the overall force composed of the combined spring force and piston force of the piston 49 of the second adjustment cylinder 35 subjected to the system pressure, the pivot lever 23 is moved toward the left, from the maximum capacity setting shown in FIG. 1, to the corresponding control setting. In order to induce this adjustment movement using a control pressure having a relatively low pressure level, the active piston surface on the piston 35 of the first adjustment cylinder 31 is selected such that it is substantially larger than that of the piston 49 of the second adjustment cylinder.

As is particularly apparent in FIG. 2, a hole 67 is formed in the piston 49 that can be subjected to the system pressure. This forms the entrance of a lubrication channel, which continues via a passage 69 in the piston rod 55, a hole 71 in the ball head 29 of the pivot lever 23 and a passage 73 in the other piston rod 41, up to the ball joint on the piston 35 of the first adjustment cylinder 31. As a result, the pressure fluid that is pressurized by the system pressure, in particular in the form of a hydraulic fluid having lubricating characteristics, can make its way as a lubricant to all the bearing surfaces of all the ball joints, such that the adjustment device 21 functions without wear, with very little friction, and reliably. 

1.(Original) An axial piston pump having a swash plate type construction, in particular for hydraulic systems, having a cylinder drum (3) that can be rotatably driven about a rotational axis (7) in a pump housing (1), in which pistons (9) are disposed such that they are axially displaceable, which support, at least indirectly, a swash plate (15) with their actuation ends (11) that are accessible outside the cylinder drum (3), which swash plate can be pivoted to a desired angle of inclination in relation to the rotational axis (7) by means of an adjustment device (21), in order to adjust the stroke of the piston (9), and thus the fluid system pressure generated by said piston, which has an adjustment piston (35) in an adjustment cylinder (31) that can be hydraulically actuated, the movement of which can be transferred to the swash plate (15) via at least one driven connection having a joint (37, 39; 29, 43), characterized in that the joint is formed by a ball joint (37, 39) located between the piston (35) and the piston rod (41) of the adjustment cylinder (31).
 2. The axial piston pump according to claim 1, characterized in that a second joint is formed by a second ball joint (29, 43) between the piston rod (41) and an actuating part (23) of the swash plate (15).
 3. The axial piston pump according to claim 1, characterized in that a spring assembly (61) is provided, that retains the ball head (29, 39) and ball socket (37, 43) of the ball joint in position, in a force-locking manner.
 4. The axial piston pump according to claim 1, characterized in that the spring assembly (61) pre-loads the swash plate (15) in the pivotal position corresponding to the maximum pump capacity.
 5. The axial piston pump according to claim 1, characterized in that a second adjustment cylinder (45) is provided, counter to the first adjustment cylinder (31) and sharing the same cylinder axis, which is perpendicular to the rotational axis (7), in that the adjustment piston (47) of the second adjustment cylinder (45) can be moved hydraulically counter to the movement of the adjustment piston (35) of the first adjustment cylinder (31), and in that the piston rod (55) of the second adjustment cylinder (45) is connected to the associated adjustment piston (47) at one end via a third ball joint (51, 53), and on the other end, together with the piston rod (41) of the first adjustment cylinder (31), forms the second ball joint (29, 43, 57) at the actuating part (23) of the swash plate (15).
 6. The axial piston pump according to claim 1, characterized in that the actuating part is formed by a pivot lever (23) connected to the swash plate (15), which extends parallel to the rotational axis (7) when set to zero pump capacity, laterally to the swash plate (15) and the cylinder drum (3), and the second ball joint (29, 43, 57) is located at its free end.
 7. The axial piston pump according to claim 1, characterized in that the spring assembly has a compression spring (61), which pre-loads the piston rod (55) of the second adjustment cylinder (45) for the movement that corresponds to the extension of the adjustment piston (49) of the second adjustment cylinder (45) and the retraction of the adjustment piston (35) of the first adjustment cylinder (31) and thus the pivoting of the pivot lever (23) from the setting in which the axes are parallel, toward the setting for the maximum pump capacity.
 8. The axial piston pump according to claim 1, characterized in that the first adjustment cylinder (31) can be subjected to a control pressure for adjusting the pump capacity, and the second adjustment cylinder (45) can be subjected to the prevailing system pressure.
 9. The axial piston pump according to claim 1, characterized in that the piston surface of the piston (35) of the first adjustment cylinder (31) that can be subjected to the control pressure is selected such that it is larger than the piston surface of the piston (49) of the second adjustment cylinder (45) that can be subjected to the system pressure.
 10. The axial piston pump according to claim 1, characterized in that ball joints on the adjustment pistons (35, 49) are formed by a ball socket (37, 51) on the respective piston (35, 49) and a ball head (39, 53) on the piston rod (41, 55).
 11. The axial piston pump according to claim 1, characterized in that the ball joint on the actuating part is formed by a ball head (29) located on the free end of the pivot lever (23) and by dome-shaped surfaces that are formed on the allocated ends of the piston rods (41, 55), and which form ball sockets (43, 57).
 12. The axial piston pump according to claim 1, characterized in that a continuous lubrication hole (67) is formed in the piston (49) that can be subjected to system pressure, which forms the entrance for a lubrication channel (69, 71, 73) for lubricating the ball joint. 